Stevens 311/Savage Arms

Is there a way to find the year of manufacture for these shotguns or at least a ballpark range?

This is a 16ga SxS with the plastic stock. Stevens 311 and Savage Arms on left. 5100 on right.
ZP circled A and circled B 7 under the barrel.
Circled 18A underside in front of trigger guard.
ZP circled A and circled B on bottom of barrels.

My reference shows it (the311) was valued @ $185 in 1984.
Made from 1981 up BUT they they had wooden stocks; later checkered.

According to my referenses; only the Stenvens 530M had the "Tenite" (plastc stock).
$120 in 1984. Discontinued about 1947.
The 530 (all had wooden stocks; except the"M" model) was superceded by the 311.

There is a note:
"Originally produced as a "Springfield" gun (the 311), this model became part of the "Stevens" line in 1948 when the "Springfield" brand name was discontinued."